1. Field of the Invention
The present invention relates to an electrode for rechargeable batteries, and more particularly to a negative electrode for secondary lithium batteries.
2. Prior Art
Active research has been conducted in order to utilize graphitized carbon as an electrode for rechargeable batteries, since it has a layered structure and forms interlayer compounds with various materials. Especially, a carbon electrode as a negative electrode for secondary lithium batteries utilizing an interlayer compound formed with lithium is expected to materialize a high capacity negative electrode free from dendrite.
The inventors of the present invention have already discovered the fact that pyrolytic carbon is advantageous to be used as a carbon electrode for the above purpose (Japanese Published Unexamined Patent Application No. 24555/1988), and pyrolytic carbon containing an iron family element is especially advantageous (Japanese Published Unexamined Patent Application No. 281673/1989).
Although the pyrolytic carbon electrode containing an iron family element has a high charge density, the inventors of the invention have recently found that some kinds of such electrodes reduce in quantity of electric charge during conservation at room temperature, specifically more than 20% of self-discharge occurs. On the other hand, a self-discharge ratio of a secondary lithium battery having a negative electrode of lithium or lithium alloy is less than 1%. In comparing these self-discharge ratios, difference is so great that the graphitized carbon electrode cannot be put into practical use.
Accordingly, an object of the present invention is to minimize a self-discharge ratio of a carbon electrode.